Since it was shown by Kohler & Milstein (Nature Vol. 256, 495-497, 1975) that it was possible to fuse mouse myeloma cells with spleen cells from immunized mice and thereby product a continuous cell line which produces a homogeneous (monoclonal) antibody, extensive attention has been focused on the production of these hybrid cell lines (hybridomas) and the monoclonal antibodies (Mabs) produced.
The development of hybridoma technology has led to a dramatically improved understanding of the antigenic molecules on the surface of human leucocytes, and over the past decade, many murine monoclonal antibodies reacting with haemopoietic cell surface antigens have been described. Following the three International Workshops on Human Leucocyte Differentiation Antigen, the majority of these antibodies have been grouped into Clusters of Differentiation (CD), and have been shown to react with restricted differentiation-lineage or maturation stage membrane antigens on lymphoid or bone marrow-derived cells (Interim Report of the 3rd Workshop Nomenclature Committee (1987) in A.J. McMichael, Ed. Leucocyte Typing III. White cell differentiation antigen. Oxford University Press, PP 949-950).
A few antibodies have been shown to have broader haemopoietic cellular reactivity. The best characterised are the antibodies fitting into CD 45 or CD 45R, which identify a family of antigens with molecular weights around 200 Kilodaltons expressed on virtually all human leucocytes (Pizzolo et al., Cancer, 1980, 46, 2640-2647; Dalchau et al., 1980, European Journal of Immunology, 10, 737-744). Other unclustered Mabs with non-lineage reactivity include PHM-1, CAMPATH-1, HuLyM3, which appear to identify separate and unique antigens (Becker et al., 1981, Pathology, 13, 669-680; Hale et al., 1983, Blood, 62, 873-882; Vaughan et al., Transplantation, 36, 446-450).